Combo respiratory pathogen tests miss pertussis

BALTIMORE – Comprehensive respiratory pathogen panels (RPAN) cannot be relied on to detect pertussis, according to an investigation from the University of Michigan, Ann Arbor.

Dr. Colleen Mayhew

Respiratory pathogen panels are popular because they test for many things at once, but providers have to know their limits, said lead investigator Colleen Mayhew, MD, a pediatric emergency medicine fellow at the University of Michigan.

“Should RPAN be used to diagnosis pertussis? No,” she said at the Pediatric Academic Societies annual meeting. RPAN was negative for confirmed pertussis 44% of the time in the study.

“In our cohort, [it] was no better than a coin flip for detecting pertussis,” she said. Also, even when it missed pertussis, it still detected other pathogens, which raises the risk that symptoms might be attributed to a different infection. “This has serious public health implications.”

“The bottom line is, if you are concerned about pertussis, it’s important to use a dedicated pertussis PCR [polymerase chain reaction] assay, and to use comprehensive respiratory pathogen testing only if there are other, specific targets that will change your clinical management,” such as mycoplasma or the flu, Dr. Mayhew said.

In the study, 102 nasopharyngeal swabs positive for pertussis on standalone PCR testing – the university uses an assay from Focus Diagnostics – were thawed and tested with RPAN.

RPAN was negative for pertussis on 45 swabs (44%). “These are the potential missed pertussis cases if RPAN is used alone,” Dr. Mayhew said. RPAN detected other pathogens, such as coronavirus, about half the time, whether or not it tested positive for pertussis. “Those additional pathogens might represent coinfection, but might also represent asymptomatic carriage.” It’s impossible to differentiate between the two, she noted.

In short, “neither positive testing for other respiratory pathogens, nor negative testing for pertussis by RPAN, is reliable for excluding the diagnosis of pertussis. Dedicated pertussis PCR testing should be used for diagnosis,” she and her team concluded.

RPAN also is a PCR test, but with a different, perhaps less robust, genetic target.

The 102 positive swabs were from patients aged 1 month to 73 years, so “it’s important for all of us to keep pertussis on our differential diagnose” no matter how old patients are, Dr. Mayhew said.

Freezing and thawing the swabs shouldn’t have degraded the genetic material, but it might have; that was one of the limits of the study.

The team hopes to run a quality improvement project to encourage the use of standalone pertussis PCR in Ann Arbor. There was no industry funding. Dr. Mayhew didn’t report any disclosures.